Process for the preparation of benzoic acid and benzoates



Il-l) Patented Apr. 23, 1935 STTES PROCESS FOR THE PRETARATION, OF

BENZOIC ACID AND BENZGATES Jules Emile Demant, Trosly Breuil, France, as-

signor to Bozel-Maltra Societ Endustrielle De Produits Chimi ues,

Guise-Laurette (Oise) France, a company of France No Drawing. Application May 18, 1933, Serial No 671,697. In France May 26, 1332 15 Claims.

The object of this invention isa process for the preparation of benzoic acid and benzoates by the oxidation of toluene with the aid of salts of hexavalent chromium at temperatures above 100 C. and under pressure, according to which process the reaction-arresting, alkaline-reacting products, such as caustic alkali, formed during the process of oxidation, are neutralized.

The inventor in his U. S. A. application No. 631,126, now Patent No. 1,945,632 dated January 30, 1934. has already proposed to use bichromates of the alkali metals or alkaline earth metals for neutralizing the aforesaid alkaline-reacting products. Even though this procedure is capable of very satisfactorily solving the question of neutralizing the alkaline-reacting substances without the addition of foreign substances, yet in the preparation of benzoates certain difficulties occasionally appear in the separation of the benzoate formed from the eliminate-containing liqucr, owing to the great solubility of both substances.

These difficulties are .overcome according to the present invention in a simple and very advantageous manner by employing for the saturation" of the alkaline-reacting compounds, forming during the oxidation of the toluene, in place of, or in addition to bichromates, for example of the alkali metals, substances which are capable of neutralizing the alkaline-reacting compounds and which at the same time ensure an easy separation of the resulting benzoic acid or benzoate from the other reaction products.

Examples of suitable additions in accordance with this invention are inorganic acids, such as sulphuric acid, or acidsalts, such as bisulphates. Organic acids, such asbenzoic acid or other organic acids, which resist the action of the chromates, are also admirably adapted for the aforesaid purpose.

If, for example, benzoic acid is employed as the acid addition, the oxidizing reaction proceeds according to the following equation:

The oxidation of the toluene proceeds surprisingly smoothly and with admirable yields, amounting to 9 to 95% and more. A pure benzoate solution is obtained as reaction product, which, when the oxidation is correctly carried out, is practically free from chromate, as well as chrcmic hydroxide, which, after filtering off and washing, is introduced into the regenerating process. One half oi the benzoate liquor is (Cl. 26ll-lil8) with advantage acidified, the free benzoic acid precipitated and employed for a fresh operation.

The other half of the reaction liquoris worked up in known manner either to benzoate by con centration or to free benzoic acid by acidifying.

- A great advantage of this method of operation is that an almost chromate-free benzoate liquor is obtained in practically quantitative yield, which has merely to be separated from insoluble chromic oxide and can be worked up without any diiiiculties arising both to benzoate and also to free acid.

A further advantageresides in the fact that the conversion can be carried out at substantially lower temperatures and pressures than hitherto.

If the operation is, for example, carried out with sodium bisulphate, the oxidation proceeds according to the f llowing equation:

A sodium benzoate liquor, containing sodium sulphate, is obtained, which is with advantage worked up by acidifying'to free benzoic acid. An alternative procedure, however, is to separate the sodium benzoate from the sodium sulphate by evaporating down the sulphate-containing liquor and subjecting the same to fractional crystallization.

When employing sulphuric acid the reaction proceeds as follows:

If the quantity of neutralizing substance added is increased to an amount corresponding to the base content of the salt of the hexavalent chro mium, free benzoic acid will be obtained as oxidation product of the toluene, instead of a hen zoate.

In this case acids, for example sulphuric acid, or acid salts, for example a bisulphate, are with advantage employed. When employing a bisul phate, such as sodium bisulphate, the reaction proceeds according to the following equation:

The reaction product obtained accordingly consists of benzoic acid, sodium sulphate and chromic hydroxide.

As oxidizing agents there may be employed both monochromates and bichromates. It need not be specifically mentioned that, when employing a monochromate, the additions must be correspondingly increased. It is advisable therefore to use bichromates as oxidizing agents. They have the advantage of being readily soluble, so that both alkali metal bichromates and alkaline earth metal bichromates can be employed, it being stated in this connection that the alkaline earth metal benzoates are also soluble.

The acid additions, which are employed according to the invention in the oxidation ofv toluene, may be added to the mixture at the: commences ment of the process of oxidation or alternatively continuously or in portions 'di-sconti'nuously during the same.

The chromic hydroxide formed during the present process may with advantage be subjected in the aqueous phase, in the presence of: bases or base-yielding substances to pressure oxidation with oxidizing gases at elevated temperatures.

The process in this case is with advantage carried: into efiect by heating. the chrornichydroxide in the-presence of water of. oxygenv or oxygencontaining gases, to temperatures above 190 C. with such a quantity of an alkali sulphate, obtained lay-product according to one of the above described modifications of the toluene oxidation, as is necessary for the formation. of an alkali bichroinate or monochromate, as well as with such a quantity of an alkaline earth oxide, hydroxide, or carbonate as is sufficient for fixing the sulphuric acid contained in the aforesaid alkali sulphate.

Besides the formation of the desired alkali bichromate or monochromate the formation of alkaline earth sulphate hereby takes place for example according to the following equations:

' It is in this way possible not only to cycle the chromium, but to utilize the alkali sulphate, obtained directly in the oxidation of toluene or by acidifying the alkali benzoate formed with sulphuric acid, for the regeneration of the bichromate or chromate.

The process according to this invention can be carried out not only with the aid of pure salts of hexavalent chromium but also with the aid of chromates, particularly chromate irits, such as are obtained by the alkaline oxidizing decomposition of chronuuin alloys, for example ferrochrome, chronuum ores or other chromium-containing substances. Aqueous suspensions or ex tracts of the aioresaid'chromate frits, to which, if desired, an equivalent quantity of acid may be added for the purpose of forming bichromates, are with advantage employed. The raw monochromates or bichromates of potassium, sodium, calcium, magnesium or the like, for example, are suitable.

In order to make better use of the oxidizing agent the toluene is with advantage employed in a small excess, for example of 5%, over the quantity calculated on the oxidizing agent present, which excess can be again recovered at the end of the operation.

Examples 1. 92 parts of pure toluene, 300 parts of sodium bichromate, 400 to 509 parts of water and 122 parts of benzoic acid are heated to 230-24? C. for about 5 to 6 hours with thorough stirring and, if necessary, any unacted upon toluene blown off with steam at the end of the reaction. The reaction material is filtered and the sodium benzoate liquor divided into two halves. One half is acidified, preferably with sulphuric acid, and the precipitated benzoic acid returned to the process. The other half is evaporated down and worked up to sodium benzoate. The mother liqu occasionally containing a little chromium, are suitably worked up to free benzoic acid. The yield amounts to to 96% of benzoic acid calculated on the toluene used up. The pr cipitated acid is obtained in a crystalline and pure form.

2.. 92 parts of pure toluene, 300 parts of sodium bichromate, 400 to 500 parts of water and M05 parts of sodium bisulphate (containing 34.85% of E2304) are heated to 230 to 240 C. for about 6 hours with. thorough stirring. If necessary, any unacted upon toluenev is blown off with steam at the end of the reaction and the reaction material filtered. The sulphate-containing sodium benzoate liquor is freed from chromic hydroxide and Worked up by concentrating and fractio-nally crystallizing to sodium benzoate or, more simply and suitably, to free benzoic acid.

260 parts of toluene and 648 parts of sodium monochromate are heated with 1,000 parts of water and 210 parts of 96% sulphuric acid in an autoclave to 220 C. for 4 to 6 hours. During this period 110 parts of sulphuric acid and 169 to 200 parts of water are introduced at uniform intervals. This is best eifected by feeding the acid continuously or in portions at definite intervals into the autoclave from a container standing under the same pressure. After the temperature has been further increased to 240 C. for 2 to 3 hours the whole is cooled down to about 50 to 6G" C., the excess of unchanged toluene distilled off, the solution filtered from the chromic hydroxide and the latter subsequently washed on the filter.

A colourless, sodium sulphate-containing sodium benzoate solution is obtained, from which the benzoic acid can either be obtained as. benzoate together with sodium sulphate by concentrating and crystallizing or can be precipitated in free form with the aid of acid, preferably sulphuri acid, in which case the sodium sulphate remains behind in the solution. The yields vary between and 98%.

If the chromic oxide-ccntaining residue is subjected, in the presence of sodium sulphate-containing liquor and an equivalent quantity of lime or calcium carbonate, to pressure oxidation in a stirring autoclave at 200 to 250 C. with the add' tion of oxygen or air, the trivalent chromium i be converted within a few hours almost quana. tatively into sodium ohromate according to the equation:

The resulting chromate liquor, after separation of the insoluble calcium sulphate, may be employed without further purification for a fresh toluene oxidation. The yield of chromium is practically quantitative.

e. 100 parts of toluene are heated for 4 to 5 hours with 300 parts of sodium bichromate and 450 to 560 parts of water in an autoclave to 226 C. with stirring. During this period a mixture of 122 parts of 30% hydrochloric acid and 10% parts of Water is at the same time introduced in tl e same manner as the sulphuric acid in Example 8.

After introducing the acid heating is continued for about 2 hours at 240 C. and the mixture thereafter cooled down to 50 to 60 C. The ex cess of toluene is then distilled off, the chromic hydroxide separated by filtration from the sodium benzoate solution and the solution worked up by concentration to sodium benzoate or by the addition of acid to free benzoic acid. The yields amount to 95 to 97%.

For the purpose of regeneration, the moist chromic oxide-containing residue is treated with 106 parts of sodium carbonate and 400 to 450 parts of water and heated in an autoclave at 100- atmospheres pressure to 250 to 300 C. for about 6 hours with stirring, whilst oxygen or air is passed through. The carbon dioxide formed is removed from the autoclave together with the gas stream.

After cooling, a pure solution of sodium bi chromate is removed from the autoclave and returned to the toluene oxidation process. The yield of chromium is practically quantitative.

5. 100 parts of toluene are heated for 5 hours to 220 C. with 294 parts of potassium bichromate and 500 parts of water in an autoclave with stilring andduring this period a solution of 125 parts of phosphoric acid, containing of HISPO-i, in 125 parts of water, introduced continuously or in portions. Heating is then continued for about 2 to 3 hours to 240 C. in order to complete the oxidation. The excess of toluene is finally distilled off.

A reaction product, consisting of chromic hydroxide, is obtained which is separated by filtration from the -mono-potassium phosphate-containing potassium benzoate liquor.

The benzoic acid is precipitated therefrom by the addition of phosphoric acid. The liquor separated from the benzoic acid is further worked up to potassium phosphates. Yield over The regeneration of the oxidizing agent is best eilected by heating the still moist chromic hydroxide-containing residue for 5 hours in a stirring autoclave to about 250to 300 C. with 225 parts of 50% potash lye and aboutv 150 parts of Water in the presence oi oxygen. The ccnversion into potassium bichroinate is quantitative.

The resulting clear potassium bichromate solution is removed from the apparatus in a hot condition. It may be employed without further purification for a fresh operation.

6. 100 parts of toluene are heated for about 4 to 5 hours with 330 parts of anhydrous magnesium monochromate, 2,000 parts of water and 105 1 parts of sulphuric acid of 66 Bel to 220 C. in an autoclave with stirring. During this period a mixture of 52 parts of sulphuric acid of 66 B. and 50 parts of water is introduced into the autoclave from a container standing under the same pressure. Heating to 240 C. is continued for a further 2 to 3 hours and the whole then cooled down to 50 to 60 C. and the excess of toluene distilled off.

After filtering on: the chromic oxide-containing residue, the magnesium sulphate-containing solution of magnesium benzoate is worked up by concentration to magnesium benzoate and magnesium sulphate. Alternatively free benzoic acid may be precipitated by the addition of sulphuric acid. Valuable magnesium sulphate may be recovered from the mother liquor. Yield over 90%.

'7. 100 parts of toluene are heated for about 4 to 5 hours with a raw calcium bichromate solution, containing 256 parts of calcium bichrornate, such as can be obtained by the oxidizing decomposition of chromium ore or chromic oxide-containing substances with the aid of lime and treating the roasted material with sulphuric acid, to 220 C. in an autoclave with stirring. An aqueous solution of sodium bisulphate, containing 49 parts of active sulphuric acid, are added during this period to the reaction material, after which heating is suitably continued for about 1 to 2 hours to 240 C. After cooling down the excess of toluene is distilled oir".

A reaction product is obtained, consisting of chromic hydroxide, calcium sulphate and an aqueous solution of sodium benzoate, which is worked up as described in the above examples. Yield over 90 to V The calcium sulphate-containing residue of chromic hydroxide is heated for about 5 hours to 250 to 300 C. in an autoclave with stirring in the presence of an aqueous lye of sodium hydr xide containing 80 parts of NaOII, and oxygen or air.

vA pure sodium bichromate solution free from silicic acid (silica), iron and alumina is obtained and worked up into a commercial article, the trivalent chromic hydroxide introduced being quantitatively recovered in the form of pure sodium bichrornate,

8. This example comprises a modification of Example 4, inwhich a mixture of 105 parts of 60% nitric acid and 105 to 200 parts of water are employed in place of the hydrochloric acid there indicated.

The benzoic acid is with advantage precipitated from the resulting sodium benzoate solution by the addition of dilute nitric acid, after which the mother liquor is worked up to sodium nitrate.

9. 92 part-sci toluene are heated for about 4 to 5 hours with 1,000 parts of toluene (as solvent for the benzoic acid formed) and with 300 parts of sodium bichroinate and 300 parts of water in an autoclave to 220 C. with stirring, a solution of 280 parts of sodium bisulphate being at the same time allowed slowly to flow in.

The mixtiue is allowed to cool and the reaction product centrifuged, washed with warm toluene and finally with water in order to displace the toluene from the solid residue.

The liquid portion of the reaction product consists of a solution of free benzoic acid in toluene and the aqueous portion of sodium sulphate. The toluene solution is freed from toluene in a vacuum and the free benzoic acid worked up in known manner.v Yield over 90%.

1 In order to regenerate the oxidizing agent, the chromic oxide-containing residue is heated for 5 hours with half of the sodium sulphate liquor formed to 250 to 300 C. in an autoclave with stirring in the presence of 56 parts of calcium oxide or '100 parts of calcium carbonate while a current of oxygen or airis passed through the apparatus.

What I claim is:

1. In a process for the preparation of benzoic acid and benzoates by the oxidation of toluene with the aid of aqueous solutions of salts of hexavalent chromium at temperatures above C. and under superatmospheric pressure and with neutralization of the alkaline-reacting products formed during the oxidation, employing at the mosta quantity of the neutralizing additions equivalent to the quantity of base present in the salt of the hexavalent chromium employed for with the aid of aqueous solutions of salts of hexavalent chromium at temperatures above 100 C.and under superatrnospheric pressure and with neutralization of the alkaline-reacting products formed during the oxidation, employing as neutralizing additions acids in quantities which at the most are equivalent to the quantity of base present in the salt of the hexavalent chromium employed for the oxidation.

3. A process according to claim 2, characterized by the use of inorganic acids as neutralizing additions.

l. A according to claim 2, characterized by the use of sulphuric acid as neutralizing addition.

5. A process according to claim 2, characterized by the use of organic acids as neutralizing additions.

6. A process by the use of tion. V

7. In a process for the preparation of benzoic acid and benzoates by the oxidation of toluene with the aid of aqueous solutions of salts of hexavalent chromium at temperatures above 100 C. and under superatrnospheric pressure and with neutraliza'ion of the alkaline-reacting products formed during the oxidation, employing as neutralizing additions acid salts in quantities which at the most are equivalent to the quantity of base present in the salt of hexavalent chromium employed for the oxidation.

8. A process according to claim 7, characterized by the use of a bisulphate as neutralizing according to claim 2, characterized benzoic acid as neutralizing addiaddition.

9. In a process for the preparation of benzoic acid and benzoates by the oxidation of toluene with the aid of aqueous solutions of salts of hexavalent chromium at temperatures above 100 C. and under superatmospheric ressure and with neutralization of the alkaline-reacting products formed during the oxidation, introducing as neutralizing additions acid agents, employed at the most in a quantity equivalent to the quantity of base present in the salt of hexavalent chromium employed for the oxidation in portions during the oxidizing process.

10. In a process for the preparation of benzoic acid and benzoates by the oxidation of toluene with the aid of aqueous solutions of salts of hexavolent chromium at temperatures above 100 C. and under superatmospheric pressure and with .eutralization of the alkaline-reacting products formed during the oxidation, employing as neutralizing addition benzoic acid, separating the resulting benzoate liquor by filtration at the end or the oxidation from the chromic hydroxide, and working up one part of the liquor to benzoic acid which is returned to the process.

11. In a process for the preparation of benzoic acid and benzoates by the oxidation of toluene with the of aqueous solutions of salts of hexavalent chro .1111 at temperatures above 100 C.

and under s..peratmospheric pressure and with train-nation of the alkaline-reacting products oxidation, using as oxidizing agent in the toluene oxidizing process chromate frits which are obtained by the alkaline oxidizing decomposition of chromium-containing substances.

22. In a process for preparation of benzoic s nd benzoates by the xidation of toluene of aqueous solutions of salts or hexavalent chromium at temperatures above 100 C. and under superatmospheric pressure and with neutralization of the alkaline-reacting products formed during the oxidation, regenerating the salts of hexavalent chromium by subjecting the chromic hydroxide formed during the toluene oxidizing process to pressure oxidation with oxidizing gases in the presence of water and of inorganic bases.

13. In a process for the preparation of benzoic and benzoates by the oxidation of toluene with the aid of aqueous solutions of salts of hexavalent chromium at temperatures above 100 C. and su; eratrnospheric pressure and with neutralization of the alkaiine-reacting products formed du ing the oxidation, regenerating the salts of avalent chromium by subjecting the chromic hydroxide formed during the toluene oxing process to pressure oxidation with oxidizthe presence of water and of inorganic substances acting as bases.

In a process for the preparation of benzoic acid and benzoates by the oxidation of toluene with the aid of aqueous solutions of salts of hexavalent chromium at temperatures above 100 C. and under superatniospheric pressure and with neutralization of the alkaline-reacting products formed during the oxidation, regenerating the salts or hexavalent chromium by treating the chromic hydroxide formed during the toluene oxidizing process at a temperature above 100 with an oxidizing gas in the presence of water and of a quantity of an alkali sulphate, obtained as lay-product during the preparation of benzoic acid, suiiicient for the formation of an alkali salt of the hexavalent chromium as well as in the presence of a quantity of an alkaline earth compound, entering into conversion with the sulphate suificient f or fixing the sulphuric acid of the alkali sulphate.

15. A process according to claim 1, characterized by theuse of toluene in a slight excess over the quantity calculated on the oxidizing agent present.

JULES EMILE DEMANT. 

